Struts – Everything You Should Know

Why are Mechanics so Keen to Replace Struts? 

There’s a term in automotive repair: “gravy”. It’s a food that tastes good and requires no effort to chew. Now I’m not saying replacing struts isn’t work. It’s physical work, a little dangerous, and time-consuming.

However, it’s predictable, which makes it profitable. It’s unlikely that something is going to go sideways during the project. It’s unlikely that we’ll get hung up waiting for a part. It’s unlikely we’ll make a mistake and need to do the job again.  

What do Struts Do? 

Let’s start with what struts do. A strut has two functions: it dampens spring oscillations like a shock absorber and supports the car’s suspension.

The Problem 

When your car drives over a bump or dip in the road, the springs compress to absorb the impact. After passing the bump, the springs extend beyond their original position. This makes the springs longer than usual, so they start to compress again. This back-and-forth movement causes the car to bounce up and down, with each bounce getting a little smaller. This can make the car feel like it’s moving in a wavy, boat-like motion.

The Solution 

A strut’s job is to control how fast the spring compresses and expands, similar to how a door closer prevents a door from slamming shut. When the strut is working properly, the spring will compress when the car goes over a bump and then return to its original position without causing the car to keep bouncing.

How is a Strut Different from a Shock? (Strut vs. Shock)

The other function of a strut, which is what separates it from a shock absorber, is that it is part of the car’s suspension. What does that mean? It basically means that the strut helps hold the car up. You cannot remove a strut from a car and continue to drive. That’s where shocks are different. You can remove a shock from a car and then drive it, it will be it will just be very bouncy. 

How do Struts Fail? 

Here’s a list of reasons for replacing a strut. Not all types of strut failures will cause noticeable symptoms.

• Lack of damping 
• Excessive leaking
• Bad bushings (knocking over bumps)
• Binding
• Being bent

If your mechanic tries to sell you struts, he should be able to clearly articulate exactly how the strut has failed. “They’re worn out.”, isn’t a good explanation. So, let’s talk about each of these and how you can evaluate, as a consumer, whether the condition is severe enough to warrant replacing the struts.  

Lack of Damping 

The most common symptom of bad struts is lack of damping and there are several ways to test for it.

The Static Bounce Method 

There are a few ways to test for lack of damping. The traditional method is to bounce the car hard by hand on one corner at a time. You should push down as hard as you can. Once the car reaches the bottom of its travel, completely release all pressure on the car and let it bounce on its own.  

If the strut is good the car will go down and then come right back up to its original position and settle. If the strut is bad, the car will continue to bounce a couple times after it comes up. 

The success of this method depends on how heavy you are and how hard you’re able to push. Cars with very stiff springs can be very difficult to test this way. Also, your car may not be durable enough to withstand a push of the required pressure. Modern cars are lightweight and don’t have big chrome bumpers. 

The Sudden Low Speed Stop Method 

This is a method I most frequently use when doing a vehicle inspection. It’s fast, more useful than the static bounce method, and doesn’t require an extended test drive.  

Here’s how to perform in the test: 

• Drive slowly (5 MPH) in an area where it’s safe to suddenly stop. 
• Suddenly stop 
• Observe how the car responds 

You’ll need to do this while driving forward for the front struts and in reverse for the rear struts. Like the static bounce test, the car should dip and then rise without continuing to bounce. You’ll be able to catch most bad struts this way. However, if a strut is marginal, you may not be able to detect it using this method. 

High-Speed Turning Test

A high-speed turning test is the most dynamic of all the tests. You’ll need to drive the car on freeway on ramps or off ramps unless you have access to a racetrack. Simply drive the car at a spirited pace through a sweeping turn. You’ll need to repeat this for a left turn and a right turn.  

If the struts are good, the car will feel solid and firmly planted while driving through the turn. If the struts are bad, you’ll notice a rocking between the outer front wheel and the inner rear wheel which will make the car feel unstable and awkward. 

Knocking Struts 

Knocking struts can be difficult to diagnose.  You may have trouble checking this on your own. However, since you know you have a noise, you know there is something wrong with the car, so you can probably trust your mechanic on this one.  

Usually, struts will only make noise in dynamic conditions, meaning they only make noise when you’re driving down the road. It’s difficult to determine exactly where the noise is coming from when you’re in the driver’s seat. 

One method to determine if a strut is the source of a knocking is to eliminate all other causes such as tie rod ends, sway bar links, control arm bushings, etc. Another method is to use a Chassis Ear. A Chassis Ear is a tool with wireless clip-on mics we connect to different suspension components to determine where the noise is loudest while driving the car. 

Binding Struts 

Binding struts can be subtle. The binding is pretty similar to damping, since it slows the movement of the strut. It’s kind of like what the strut is supposed to be doing, except it’s caused by mechanical friction rather than hydraulic damping. The main differences are consistency and returning to a neutral position.  

Bent Struts 

Struts can get bent if the car is hit, drives over a curb, or has some other trauma. Mechanics usually find this while aligning a car and there’s not easy way for you to confirm it. 

When Are Struts Unsafe? 

The chain stores go hard on the safety issue. I’ve seen a repair order where the service advisor made his customer sign a statement saying they agree to tow the car out before they return the keys.  

This sort of thing is just high-pressure sales tactics. Pretending to be concerned about getting sued for releasing a car is sleazy. As mechanics we are under no obligation to prevent anyone from driving a vehicle even if we believe it to be unsafe. It is not our responsibility, nor is it within our authority. 

So, what’s unsafe? Where’s the line? I’d advise using common sense for this decision. Let’s say you have a Toyota Corolla with poor damping on one of the front struts. Will the car perform as well as a Toyota Corolla with good struts? No, it won’t. However, I guarantee it handles better than a UPS truck in perfect condition. So, if the Toyota Corolla with a bad strut is unsafe, wouldn’t it follow that UPS trucks are also unsafe?  

So, use common sense. If you feel like you’re having difficulty controlling the car under the conditions you’re driving in, then don’t drive it. 

Should you replace your struts at 50,000 miles? 

On Monroe’s website (a strut manufacturer) they made the following statement: “Experts recommend having your vehicle’s shocks and struts inspected every 12,500 miles and replaced every 50,000* miles. 

Experts in what? Selling unnecessary repair work? I took a few minutes to try to find any scientific support for this claim. The closest I came was the Automotive Maintenance Repair Association’s claim that: 

“Laboratory and field testing show that most strut and shock (ride control) units installed during a vehicle’s initial assembly – as Original Manufacturer’s Equipment (OEM), degrade measurably by 50,000 miles (80,000 kilometers).” 

So “Experts” and “Laboratory and field testing”. Who are these experts? Where is this lab? Where’s this data? I had ChatGPT 4o go looking for the information in case I had missed something. It found pretty much the same thing; lots of people making the claim that struts need to be replaced at 50,000 miles with no proof or sources cited whatsoever. 

Now, in fairness to Monroe, they may be talking about their own product, which is garbage. It’s entirely possible their struts won’t last over 50K. However, the likelihood of Toyota, Honda, Subaru, or Mazda needing struts at 50K is VERY low.  

Strut Replacement Cost

The price to replace struts is going to be different for different cars in several ways:

• cost of parts
• difficulty of the job (labor time)
• parts worn/needed

So, unfortunately you can’t just search “how much do struts cost” and get a real answer. If you want to make sure you’re getting a reasonable quote for a strut job, you’ll need to call around and compare. However, this can be tricky. Please read our old (but still valid) article on shopping for automotive repair and maintenance.

The key points are:

• make sure you’re comparing job (all parts and labor items the same)
• make sure you know the brand of the parts because this can have a huge impact on cost

Can I Replace my Own Struts? 

I’m not going to tell anybody they can’t do something. I’ve many customers pull off some amazing DIY projects. I could probably write another article about some of the cool mechanical things I’ve seen non-mechanics do. 

If you want to know how to replace struts, check for a service manual online and a YouTube video for your model. If you do this and think, “hey replacing struts is something I can do”, here’s a bit of advice: don’t buy pre-assembled strut assemblies. 

So far, I have not seen one that’s good quality. If you buy a KYB pre-assembled unit, the strut will be fine; it will be a nice KYB strut. However, the top mount and spring will likely be junk. It’s likely that you would be much better off keeping your stock spring and stock strut mount. We have seen tons of newish pre-assembled struts fail. 

The reason pre-assembled struts are popular with the DIY crowd is that there’s no need to have a special tool to compress the strut spring. The other reason is that the cost is low. Often lower than buying a strut and having a shop swap the springs and mounts for you.  

Alignment After Strut Replacement

Do you need an alignment after replacing the struts? Yes is the short answer. If you skip the alignment you’ll still be able to drive the car. In fact, there may be no noticeable symptom. However, just because the car doesn’t pull or drift doesn’t mean the alignment is ok. You may not find that out your alignment was off until the tires wear out prematurely, and then it’s too late, for that set of tires at least.

Both camber and toe will typically be affected when the struts are removed and replaced. This is true even when the same struts are removed and put back on, but is even more true when new struts are installed.

How Long Does it Take to Replace Struts?

Replacing struts is usually a one day project. It doesn’t take a mechanic a day to do the work, but at our shop all cars are dropped off for the day. Actual time ranges from 2 hours to (in a few extreme cases) 8 hours. Some shops work with a while you wait model, so how long you’ll need to leave your car will vary depending on the car.

Normally we’ll order parts ahead of your appointment. However, sometimes we’ll find other issues (like worn strut top mounts or sagging springs) that should be addressed while the struts are out. This is why we prefer to check the struts ourselves prior to the appointment rather than relying on another shop’s diagnosis. Depending on parts availability, this may delay the project.

Do I Need to Replace my Struts? 

Hopefully you can now form your own opinion and don’t need to rely on someone with a vested interest in you buying stuff. If someone says you need struts, it’s fine to ask why. If it’s something you can verify on your own, go ahead. It’s fine to reschedule work until you’ve had time to think and evaluate. If you start getting pressured, your mechanic is probably sleazy. Get a second opinion.